A number of bed wetting alarms exist in the prior art. They typically sense the presence of urine by its electrical conductivity, creating an electrical signal which is then used to set off an alarm. The alarm, typically a buzzer or other audible alarm, must wake the user as quickly as possible after urine has been detected in order to minimize the necessary user response, and to facilitate the user's, learning to avoid bedwetting.
The problem is that audible alarms must be remote from the sensor because their sound is muffled by passage through bedding, clothing etc. This requires that the alarm be connected to the sensor by wires or in some cases radio signals. In order that the alarm wake the user quickly, it often remoted to a bedside nightstand or in some cases to a shoulder-top location. But the variability in the user's sleeping position makes precise control of the decibel level at the user's ear impossible. Thus very loud alarms must be used, especially for deep sleepers, to compensate for unpredictable muffing of the sound of the alarm. While the extent to which a pillow or other article can muffle such alarms is in practice too great to overcome, the very attempt to do so results in a potential for hearing loss when said muffling does not take place. And in general, the ability of even an earpiercing alarm to wake a deep sleeper is often inadequate.
In any case, the awkwardness and risk of entanglement inherent in use of wires around a sleeping child makes the use of such alarms much less attractive.